Cytotoxic Effects of Intranasal Midazolam on Nasal Mucosal Tissue.

The aim of this experimental study was to investigate the cytotoxic effects of intranasal midazolam on nasal mucosal tissue in rats. Forty healthy rats were randomly divided into 5 groups. Group 1 (n = 8) was the control group, group 2 (n = 8) received intranasal saline, group 3 (n = 8) received intranasal midazolam, group 4 (n = 8) received intraperitoneal saline, and group 5 received intraperitoneal midazolam (n = 8). Midazolam and saline were administered via intraperitoneal and intranasal routes at doses of 200 µg/kg. Nasal septal mucosal stripe tissues were removed at the 6th hour. All materials were evaluated according to Ki67 and p53 staining to evaluate proliferation and apoptosis, respectively, and hemotoxylin and eosin staining was performed for histopathology evaluation. Ki67 values and inflammation in group 3 were statistically higher compared to group 1, group 2, and group 4. P53 values in group 3 were statistically higher compared to group 1. Assessment of subepithelial edema between group 3 and the other groups revealed no statistically significant differences. Assessment of cilia loss between group 3 and group 1, group 2, and group 4 revealed no statistically significant difference. The evaluation of goblet cell loss between group 3 and group 1 revealed a statistically significant difference. Intranasal midazolam had adverse effects on nasal mucosa. However, intranasal midazolam is as safe as systemic midazolam administration with respect to nasal mucosa.

[Comparison of dexmedetomidine and midazolam on neurotoxicity in neonatal mice].

Dexmedetomidine and midazolam have been widely used in clinical anesthesia and intensive care unit sedation. These two drugs differ in sedative mechanism. We hypothesized that the neurotoxicity of repeated exposure to dexmedetomidine or midazolam for neonatal mice might be different. Twenty four mice of postnatal day 8 were randomly divided into control (n=8), dexmedetomidine (n=8) and midazolam group (n=8) respectively. In the three groups, saline(10mL/kg), dexmedetomidine(10microg/kg) or midazolam(40mg/kg) was injected intraperitoneally once a day, in the next five days, respectively. Then the brains of the mice in the three qroups were removed and cryosectioned. Apoptotic neural cell in hippocampus region was detected with terminal deoxynucleotydyl transferase -mediated dUTP nick end labeling(TUNEL). Bcl2 and Bax protein expression level in the hippocampus were determined by immunofluorescent staining. In the present study, the number of TUNEL-positive cells from midazolam group ((20 +/-3) /mm2) was larger than that from dexmedetomidine group ((15+/-2) /mm2, P<0. 05) and control group((13+/-3) /mm2, P<0. 05); Bcl-2 protein quantity in hippocampus from control group((790+/-103)/mm2)was significantly lower than that in midazolam group((1187+/- 162)/mm2, P<0.05)and dexmedetomidine group((890+/-125)/mm2, P<0. 05). Bax protein level in control group((942+/-104)/mm2) was also significantly lower than that in midazolam group((1839+/-160)/mm2, P<0. 05)and dexmedetomidine group((1143+/-125)/mm2, P<0. 05); Bax/Bcl-2 ratio in midazolam group(0. 64+/-0. 13) was significantly lower than that in dexmedetomidine group(0. 78 +/-0. 14, P<0. 05) and control group(0. 84+/-0. 15, P<0. 05). Our results suggest that dexmedetomidine has lower neurotoxicity than midazolam for neonatal mice.

Corneal lesions related to an anesthetic mixture of medetomidine, midazolam, and butorphanol treatment in rats.

An anesthetic mixture of medetomidine, midazolam and butorphanol (MMB) has been recently used in laboratory animals. We observed corneal opacity in nephrectomized rats that had undergone two operations under MMB anesthesia at 4 and 5 weeks of age. To evaluate the features of this corneal opacity, ophthalmic examinations were conducted in 83 nephrectomized rats, and 8 representative animals with corneal opacity were evaluated histopathologically 4 weeks after operation. The ophthalmic examinations revealed that 66/83 animals had corneal opacity, which was characterized histopathologically by mineralization with or without inflammation in the corneal stroma. In addition, to examine the possible causes of this corneal opacity, we investigated whether similar corneal changes were induced by the MMB anesthetic treatment in normal rats. The MMB anesthetic was administered twice to 4- and 5-week-old normal SD rats (5 animals/age) in the same manner as for the nephrectomized rats. Ophthalmic examinations were conducted in all the animals once a week, and the animals were necropsied 4 weeks after the first administration. In normal rats, similar corneal opacity was observed after the first administration, and increases in the severity and size of the corneal opacity were noted after the second administration. In conclusion, this study revealed the features of corneal opacity in rats undergoing nephrectomy under MMB anesthesia and the occurrence of similar corneal opacity in normal rats treated with MMB anesthetic. To the best of our knowledge, this is the first report of corneal opacity related to MMB anesthetic treatment in rats.

Additives in intravenous anesthesia modulate pulmonary inflammation in a model of LPS-induced respiratory distress.

BACKGROUND: It has been suggested that propofol with ethylenediaminetetraacetic acid (EDTA) can modulate the systemic inflammatory response. Prolonged higher levels of pulmonary inflammation are associated with poor outcome of patients with acute lung injury. In the present study, we hypothesized that pulmonary inflammation could be modulated by propofol with EDTA compared with propofol with sulfite. METHODS: Respiratory distress was induced in rats (n=25) by intratracheal nebulization of lipopolysaccharide (LPS). After 24 h, animals were randomized to either propofol with EDTA (Propofol(EDTA)), propofol with sulfite (Propofol(sulfite)) or ketamine/midazolam (Ket/Mid); control animals received saline (n=30). Animals were ventilated for 4 h and blood gases were measured hourly. Bronchoalveolar lavage (BAL) was performed for cytokine analysis of: tumor necrosis factor (TNF), interleukin (IL)-6 and macrophage inflammatory protein (MIP)-2. RESULTS: LPS led to increased pulmonary inflammation in all groups compared with the control groups. Gas exchange deteriorated over time only in the LPS Propofol(sulfite) group and was significantly lower than the Ket/Mid group. Only IL-6 was significantly higher in the LPS Propofol(sulfite) group compared with both the Ket/Mid group and the Propofol(EDTA) group. CONCLUSION: Pulmonary IL-6 can be modulated by additives in systemic anesthesia. IMPLICATION STATEMENT: This study demonstrates that pulmonary inflammation caused by direct lung injury can be modulated by intravenous anesthesia used in critically ill patients.

Testing for midazolam and oxycodone in blood after formalin-embalmment: About a complex medico-legal case.

The stability of compounds in formalin solution is an important factor for drug analysis in a toxicological investigation. In this article, the authors report a complex medico-legal case involving midazolam and oxycodone. The complexity of this case comes from the fact that the body was embalmed with formalin solution before the autopsy. This technique, called thanatopraxy, allows the preservation of corpses from decomposition, the destruction of a maximal number of micro-organisms, and the presentation of the body with a natural appearance to the family. Unfortunately, when thanatopraxy is performed before the collection of biological specimens, the toxicological results are not representative of the time of the death. In addition, the interpretation of the results is difficult, because formalin can cause oxidation of xenobiotics present in the body at the time of the death, alter the pH of the tissues and dilute the compounds. To document the chemical stability of midazolam and oxycodone in formalin solution and interpret the results, a stability study was conducted for 21 days. Blood containing midazolam and oxycodone was spiked with formalin, kept at 4°C and regularly tested for both drugs. This study showed a rapid degradation of midazolam and oxycodone (85% during the first 24 hours for oxycodone). In the peripheral blood of the victim, methanol (1.31 g/L), midazolam (74ng/mL) and oxycodone (152 ng/mL) were identified. According to the stability study, the measured concentrations in formalin fixed-tissues are to be interpreted very carefully, knowing that significant degradation has occurred.

Early Developmental Exposure to Repetitive Long Duration of Midazolam Sedation Causes Behavioral and Synaptic Alterations in a Rodent Model of Neurodevelopment.

There is a large body of preclinical literature suggesting that exposure to general anesthetic agents during early life may have harmful effects on brain development. Patients in intensive care settings are often treated for prolonged periods with sedative medications, many of which have mechanisms of action that are similar to general anesthetics. Using in vivo studies of the mouse hippocampus and an in vitro rat cortical neuron model we asked whether there is evidence that repeated, long duration exposure to midazolam, a commonly used sedative in pediatric intensive care practice, has the potential to cause lasting harm to the developing brain. We found that mice that underwent midazolam sedation in early postnatal life exhibited deficits in the performance on Y-maze and fear-conditioning testing at young adult ages. Labeling with a nucleoside analog revealed a reduction in the rate of adult neurogenesis in the hippocampal dentate gyrus, a brain region that has been shown to be vulnerable to developmental anesthetic neurotoxicity. In addition, using immunohistochemistry for synaptic markers we found that the number of presynaptic terminals in the dentate gyrus was reduced, while the number of excitatory postsynaptic terminals was increased. These findings were replicated in a midazolam sedation exposure model in neurons in culture. We conclude that repeated, long duration exposure to midazolam during early development has the potential to result in persistent alterations in the structure and function of the brain.

Disruption of brain MEK-ERK sequential phosphorylation and activation during midazolam-induced hypnosis in mice: Roles of GABAA receptor, MEK1 inactivation, and phosphatase MKP-3.

Midazolam is a positive allosteric modulator at GABAA receptor that induces a short hypnosis and neuroplasticity, in which the sequential phosphorylation of MEK1/2 and ERK1/2 was shown to play a role. This study investigated the parallel activation of p-MEK and p-ERK and regulatory mechanisms induced by midazolam through the stimulation of GABAA receptors in the mouse brain. During the time course of midazolam (60mg/kg)-induced sleep in mice (lasting for about 2h) p-Ser217/221 MEK1/2 was increased (+146% to +258%) whereas, unexpectedly, p-Tyr204/Thr202 ERK1/2 was found decreased (-16% to -38%), revealing uncoupling of MEK to ERK signals in various brain regions. Midazolam-induced p-MEK1/2 upregulation was prevented by pretreatment (30min) with flumazenil (10mg/kg), indicating the involvement of GABAA receptors. Also unexpectedly, midazolam-induced p-ERK1/2 downregulation was not prevented by flumazenil (10 or 30mg/kg). Notably, during midazolam-induced sleep the content of inactivated p-Thr286 MEK1, which can dampen ERK1/2 activation, was increased (+33% to +149%) through a mechanism sensitive to flumazenil (10mg/kg). Midazolam also increased MKP-3 (+13% to +73%) content and this upregulation was prevented by flumazenil (10mg/kg); an effect suggesting ERK inactivation because MKP-3 is the phosphatase selective for ERK1/2 dephosphorylation. The results indicate that during midazolam-induced sleep in mice there is an uncoupling of p-MEK (increased) to p-ERK (decreased) signals. p-ERK1/2 downregulation (not involving GABAA receptors) is the result of increased inactivated MEK1 and phosphatase MKP-3 (both effects involving GABAA receptors). These findings are relevant for the neurobiology and clinical use of benzodiazepines.

Effects of pentobarbital, isoflurane, or medetomidine-midazolam-butorphanol anesthesia on bronchoalveolar lavage fluid and blood chemistry in rats.

Bronchoalveolar lavage fluid (BALF) is commonly examined for pulmonary toxicity in animal studies. Two common means of anesthesia before euthanasia and bronchoalveolar lavage in rats are intraperitoneal injection of pentobarbital and inhalation of isoflurane. Medetomidine-midazolam-butorphanol is an alternative anesthesia to pentobarbital for animal welfare; however, the effect of this combination on BALF and blood chemistry is unknown. Here, we compared the effects of anesthesia by intraperitoneal injection of pentobarbital or one of two combinations of medetomidine-midazolam-butorphanol (dose, 0.375-2.0-2.5 or 0.15-2.0-2.5 mg/kg) or by inhalation of isoflurane on BALF and blood chemistry in rats with or without pulmonary inflammation. In BALF, we determined total protein, albumin, lactate dehydrogenase, total cell count and neutrophil count. In serum, we conducted a general chemistry screen. After anesthesia with pentobarbital or isoflurane, there were no significant differences between any of the BALF or blood chemistry parameters with or without inflammation. After anesthesia with either of the combinations of medetomidine-midazolam-butorphanol, lactate dehydrogenase, total cell count, neutrophil count, and almost all of the blood chemistry parameters were comparable with those observed after pentobarbital or isoflurane; however, BALF albumin and serum glucose were significantly increased in rats without inflammation. After the combination of low-dose medetomidine in rats with inflammation, BALF parameters were comparable with those observed after pentobarbital or isoflurane. Our results show that, of the anesthetics examined, inhalation of isoflurane is the most appropriate means of anesthesia when examining BALF or serum for toxicity studies in rats.

Early exposure to common anesthetic agents causes widespread neurodegeneration in the developing rat brain and persistent learning deficits.

Recently it was demonstrated that exposure of the developing brain during the period of synaptogenesis to drugs that block NMDA glutamate receptors or drugs that potentiate GABA(A) receptors can trigger widespread apoptotic neurodegeneration. All currently used general anesthetic agents have either NMDA receptor-blocking or GABA(A) receptor-enhancing properties. To induce or maintain a surgical plane of anesthesia, it is common practice in pediatric or obstetrical medicine to use agents from these two classes in combination. Therefore, the question arises whether this practice entails significant risk of inducing apoptotic neurodegeneration in the developing human brain. To begin to address this problem, we have administered to 7-d-old infant rats a combination of drugs commonly used in pediatric anesthesia (midazolam, nitrous oxide, and isoflurane) in doses sufficient to maintain a surgical plane of anesthesia for 6 hr, and have observed that this causes widespread apoptotic neurodegeneration in the developing brain, deficits in hippocampal synaptic function, and persistent memory/learning impairments.

Potential of ketamine and midazolam, individually or in combination, to induce apoptotic neurodegeneration in the infant mouse brain.

Recently, it was reported that anesthetizing infant rats for 6 h with a combination of anesthetic drugs (midazolam, nitrous oxide, isoflurane) caused widespread apoptotic neurodegeneration in the developing brain, followed by lifelong cognitive deficits. It has also been reported that ketamine triggers neuroapoptosis in the infant rat brain if administered repeatedly over a period of 9 h. The question arises whether less extreme exposure to anesthetic drugs can also trigger neuroapoptosis in the developing brain. To address this question we administered ketamine, midazolam or ketamine plus midazolam subcutaneously at various doses to infant mice and evaluated the rate of neuroapoptosis in various brain regions following either saline or these various drug treatments. Each drug was administered as a single one-time injection in a dose range that would be considered subanesthetic, and the brains were evaluated by unbiased stereology methods 5 h following drug treatment. Neuroapoptosis was detected by immunohistochemical staining for activated caspase-3. It was found that either ketamine or midazolam caused a dose-dependent, statistically significant increase in the rate of neuroapoptosis, and the two drugs combined caused a greater increase than either drug alone. The apoptotic nature of the neurodegenerative reaction was confirmed by electron microscopy. We conclude that relatively mild exposure to ketamine, midazolam or a combination of these drugs can trigger apoptotic neurodegeneration in the developing mouse brain.

Reducing risk of overdose with midazolam injection in adults: an evaluation of change in clinical practice to improve patient safety in England.

RATIONALE AIMS AND OBJECTIVES: This study sought to evaluate potential reductions in risk associated with midazolam injection, a sedating medication, following a UK National Patient Safety Alert. This alert, 'Reducing risk of overdose with midazolam injection in adults', was sent to all National Health Service organizations as a Rapid Response Report detailing actions services should take to minimize risks. METHOD: To evaluate any potential changes arising from this alert, a number of data sources were explored including reported incidents to a national reporting system for health care error, clinician survey and audit data, pharmaceutical purchasing patterns and feedback from National Health Service managers. RESULTS: Prior to the Rapid Response Report, 498 incidents were received by the National Patient Safety Agency including three deaths. Post-implementation of the Rapid Response Report (June 2009), no incidents resulting in death or severe harm had been received. All organizations reported having completed the Rapid Response Report actions. Purchase and use of risk-prone, high-strength sedating midazolam by health care organizations decreased significantly as did the increased use of safer, lower strength doses (as recommended in the Rapid Response Report). CONCLUSIONS: Organizations can achieve safer medication practices, better knowledge, awareness and implementation of national safer practice recommendations. Risks from inadvertent overdose of midazolam injection were reduced post-implementation of national recommendations. Ongoing monitoring of this particular adverse event will be required with a sustained patient safety message to health services to maintain awareness of the issue and reduction in the number of midazolam-related errors.

Early Exposure to General Anesthesia Disrupts Spatial Organization of Presynaptic Vesicles in Nerve Terminals of the Developing Rat Subiculum.

Exposure to general anesthesia (GA) during critical stages of brain development induces widespread neuronal apoptosis and causes long-lasting behavioral deficits in numerous animal species. Although several studies have focused on the morphological fate of neurons dying acutely by GA-induced developmental neuroapoptosis, the effects of an early exposure to GA on the surviving synapses remain unclear. The aim of this study is to study whether exposure to GA disrupts the fine regulation of the dynamic spatial organization and trafficking of synaptic vesicles in presynaptic terminals. We exposed postnatal day 7 (PND7) rat pups to a clinically relevant anesthetic combination of midazolam, nitrous oxide, and isoflurane and performed a detailed ultrastructural analysis of the synaptic vesicle architecture at presynaptic terminals in the subiculum of rats at PND 12. In addition to a significant decrease in the density of presynaptic vesicles, we observed a reduction of docked vesicles, as well as a reduction of vesicles located within 100 nm from the active zone, in animals 5 days after an initial exposure to GA. We also found that the synaptic vesicles of animals exposed to GA are located more distally with respect to the plasma membrane than those of sham control animals and that the distance between presynaptic vesicles is increased in GA-exposed animals compared to sham controls. We report that exposure of immature rats to GA during critical stages of brain development causes significant disruption of the strategic topography of presynaptic vesicles within the nerve terminals of the subiculum.

Early Exposure to General Anesthesia with Isoflurane Downregulates Inhibitory Synaptic Neurotransmission in the Rat Thalamus.

Recent evidence supports the idea that common general anesthetics (GAs) such as isoflurane (Iso) and nitrous oxide (N2O; laughing gas) are neurotoxic and may harm the developing mammalian brain, including the thalamus; however, to date very little is known about how developmental exposure to GAs may affect synaptic transmission in the thalamus which, in turn, controls the function of thalamocortical circuitry. To address this issue we used in vitro patch-clamp recordings of evoked inhibitory postsynaptic currents (eIPSCs) from intact neurons of the nucleus reticularis thalami (nRT) in brain slices from rat pups (postnatal age P10-P18) exposed at age of P7 to clinically relevant GA combinations of Iso and N2O. We found that rats exposed to a combination of 0.75 % Iso and 75 % N2O display lasting reduction in the amplitude and faster decays of eIPSCs. Exposure to sub-anesthetic concentrations of 75 % N2O alone or 0.75 % Iso alone at P7 did not affect the amplitude of eIPSCs; however, Iso alone, but not N2O, significantly accelerated decay of eIPSCs. Anesthesia with 1.5 % Iso alone decreased amplitudes, caused faster decay and decreased the paired-pulse ratio of eIPSCs. We conclude that anesthesia at P7 with Iso alone or in combination with N2O causes plasticity of eIPSCs in nRT neurons by both presynaptic and postsynaptic mechanisms. We hypothesize that changes in inhibitory synaptic transmission in the thalamus induced by GAs may contribute to altered neuronal excitability and consequently abnormal thalamocortical oscillations later in life.

Neurotoxicity of midazolam in the rabbit.

Safe and efficient use of spinal drugs requires neurotoxicologic animal studies before ethical application. We have evaluated the neurotoxicologic interruptions of intrathecal administration of midazolam in rabbits. Eighteen white New Zealand rabbits were randomly assigned into three groups consisting of six rabbits each. In conscious animals, 0.3 ml 0.9% normal saline solution, 0.3 ml 0.1% midazolam (Roche, Dormicum) or 0.3 ml preservative free midazolam were intrathecally administered. Light and fluorescence microscopy evaluations were performed on transverse spinal cord sections by a neurohistopathologist in a blind fashion. Midazolam and preservative free midazolam treated rabbits showed significant histologic changes in light and fluorescence microscopy. The histologic and vascular lesions with the use of midazolam and preservative free midazolam suggested neurotoxic effects; thus chronic intrathecal administration of midazolam should be avoided in humans.

Stable low-rate midazolam self-injection with concurrent physical dependence under conditions of long-term continuous availability in baboons.

The current research was undertaken to characterize intravenous midazolam self-injection and the concurrent development of physical dependence under conditions of continuous drug availability. Baboons (n=6) i.v. self-injected midazolam under conditions of continuous availability under a fixed-ratio 30 schedule of lever-pull responses with a 5-min time-out after each injection. Midazolam (1.0 mg/kg) maintained an orderly spaced within-day pattern of injections and low, but stable, daily rates of self-injection over 30 or more days (e.g. <20 injections/day). Sequential substitution of saline and then midazolam produced rapid extinction and then reinstatement of responding at the same stable rate. In subsequent manipulations, a range of lower doses of midazolam (0.0156-0.25 mg/kg) were also shown to reinstate self-injection responding after extinction on saline; however, both chronic and acute dose manipulations indicated that dose-regulation was poor. Chronic self-injection of the high dose (1.0 mg/kg) but not lower doses produced a suppression in responding maintained by food pellet delivery. Chronic self-injection of 1.0 and 0.25 mg/kg midazolam produced physical dependence as reflected in classic benzodiazepine spontaneous and flumazenil-precipitated withdrawal syndromes, including tremor, vomiting and, in one instance, seizure. The stable, low-rate self-injection of midazolam, with concurrent development of physical dependence, demonstrated in the present study may provide a useful model system for investigating factors which contribute to long-term inappropriate use of benzodiazepines by physically dependent patients.

Buprenorphine and midazolam act in combination to depress respiration in rats.

High dose buprenorphine is used as substitution treatment in human heroin addiction. Deaths have been reported in addicts using buprenorphine, frequently in association with benzodiazepines. In the current study, we observed the effects of buprenorphine and midazolam alone and in combination on arterial blood gases. Four groups of 10 male Sprague-Dawley rats received a parenteral injection of aqueous solvent, buprenorphine (30 mg/kg, iv), midazolam (160 mg/kg, ip), or buprenorphine (30 mg/kg, iv) plus midazolam (160 mg/kg, ip). Serial blood gases were obtained over 3 hours. There was a mild but significant effect of buprenorphine alone in comparison with the aqueous solvent on PaCO2 at 60 min (6.24 vs. 5.65 kPa, p< 0.01). There was also a mild but significant effect of midazolam alone in comparison with aqueous solvent on arterial pH at 90 min (7.33 vs. 7.41,p< 0.001) and PaCO2 at 60 min (6.52 vs. 5.65 kPa,p< 0.01). The combination of midazolam and buprenorphine produces a rapid, profound, and prolonged respiratory depression, as demonstrated by an increase in PaCO2 at 7.65 +/- 0.12 kPa at 20 min and a decrease in arterial pH at 7.25 +/- 0.02 at 20 min, with appearance of delayed hypoxia with a decrease in PaO2 at 8.74 +/- 0.20 kPa at 120 min. These data show that high doses of midazolam and buprenorphine alone have limited effects on arterial blood gases in rats while midazolam and buprenorphine appear to act in an additive or synergistic fashion to depress ventilation in rats.

Construction of Salmonella typhimurium YG7108 strains, each coexpressing a form of human cytochrome P450 with NADPH-cytochrome P450 reductase.

A series of Salmonella typhimurium (S. typhimurium) YG7108 strains, each coexpressing a form of human cytochrome P450 (CYP) (CYP1A1, CYP1A2, CYP1B1, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, or CYP3A5) together with human NADPH-cytochrome P450 reductase (OR), was established. The parental S. typhimurium YG7108, derived from TA1535, lacks two O(6)-methylguanine-DNA methyltransferase genes, ada and ogt, and is highly sensitive to the mutagenicity of alkylating agents. The expression levels of CYP holo-protein in the genetically engineered S. typhimurium YG7108 cells, determined by carbon monoxide (CO) difference spectra, ranged from 62 nmol/L culture for CYP2C19 to 169 nmol/L culture for CYP3A4. The expression level of the OR varied, depending on the form of CYP coexpressed, and ranged from 214 to 1029 units/L culture. Each form of CYP expressed in the S. typhimurium YG7108 cells catalyzed the oxidation of a representative substrate at an efficient rate. The rates appeared comparable to the reported activities of CYP expressed in human liver microsomes or CYP in other heterologous systems, indicating that the OR was sufficiently expressed to support the catalytic activity of CYP. These S. typhimurium strains may be useful not only for predicting the metabolic activation of promutagens catalyzed by human CYP but also for identifying the CYP form involved.

FG 7142- and restraint-induced alterations in the ataxic effects of alcohol and midazolam in rats are time dependent.

The purpose of this study was to examine whether acute stress exposure would alter the ataxic properties of midazolam or ethanol in rats. Rats were administered either vehicle or FG 7142 (10 mg/kg) and placed back in their home cages, or placed in restraining tubes for 90 min. Three and one-half or 24 h following injection all subjects were then administered an ataxic dose of either ethanol or midazolam and after 10 min, motoric impairment was assessed by rotarod performance. Neither FG 7142 administration nor restraint had an impact on rotarod performance 3-1/2 h later for ethanol nor 24 h later in response to midazolam. However, midazolam-induced ataxia was significantly modified 3-1/2 h following both restraint and FG 7142 exposure. Similarly, at the 24-h time point, both manipulations had a significant effect on ethanol-induced motor incoordination. Importantly, prior exposure to FG 7142 and restraint was without effect on rotarod performance in saline-treated subjects. Functional alterations in behavioral reactivity to low doses of two classes of CNS depressants by the acute stress of restraint and/or FG 7142 administration suggest the anxiogenic nature of these stressors may be the critical factor.

Sustained synergism by chronic caffeine of the motor control deficit produced by midazolam.

To evaluate the effects of chronic caffeine on the impairment of discriminative fine motor control produced by midazolam, rats were trained to hold a force transducer steady to deliver food pellets. Chronic, daily doses of midazolam (3 mg/kg SC) led to a stable level of motor impairment. Chronic caffeine (20 mg/kg IP) alone usually produced a more moderate deficit or, for one animal, no deficit. Combined, chronic administration of these doses yielded a sustained synergism in motor performance impairment, which contrasted with the antagonism usually found between the benzodiazepines and methylxanthines when performance is evaluated by psychomotor tests not requiring fine motor control. The observed synergism was not explicable in terms of measured disposition of the drugs. The synergistic production of fine motor dyskinesia by the concurrent administration of caffeine and midazolam may be relevant to the triggering of anxiety attacks by caffeine observed in panic disorder patients.

Chronic bretazenil produces tolerance to chlordiazepoxide, midazolam, and abecarnil.

The purpose of the present study was to determine if chronic treatment with a nonsedative benzodiazepine partial agonist would confer tolerance to the rate-decreasing effects of other benzodiazepine ligands in a fixed-interval procedure in rats. A separate group of rats was treated chronically with the sedative benzodiazepine full agonist, chlordiazepoxide, for comparison. It was hypothesized that tolerance would develop rapidly to chlordiazepoxide due to loss of reinforcement density at rate-decreasing doses and that there would probably be cross-tolerance to other rate-decreasing benzodiazepine ligands such as midazolam and abecarnil. Because bretazenil does not produce rate decreases, however, it was not expected that tolerance would be found to chlordiazepoxide, midazolam, or abecarnil. After 8-12 weeks of chronic treatment with either chlordiazepoxide or bretazenil, however (final dose of benzodiazepine = 30 mg/kg/day), tolerance was found to the rate-decreasing effects of chlordiazepoxide, midazolam, and abecarnil in both groups. It is concluded that such tolerance was most likely due to a saturation of benzodiazepine receptors by this high-affinity partial agonist.